The objective of this project is the research and development of analytical methods which are used to: (1) establish the structure and purity of new antitumor agents and their metabolites, (2) determine physical and chemical properties of new anticancer drugs, (3) quantitate drugs and their metabolites in biological samples to elucidate pharmacology and to determine pharmacokinetics, and (4) study reaction mechanisms of potentially useful synthetic transformations. Mass spectrometry, gas chromatography and high- performance liquid chromatography, either alone or in combination, are emphasized techniques. Compounds of current interest are cytidine analogs, modified nucleosides, oligonucleotides and differentiating agents.